1. Field of the Invention
The present invention relates to a coaxial connector to be connected with a coaxial cable.
2. Description of the Related Art
Where using a coaxial cable, there arises a problem of matching between the characteristic impedances of the coaxial cable and of an object connected to the cable. If the characteristic impedances do not match, a reflection wave occurs at the connection point of the coaxial cable, deteriorating the VSWR (voltage standing wave ratio). Accordingly, it is a practice to use a coaxial cable having characteristic impedance appropriate for an object being connected thereto. For a coaxial connector to be connected with such a coaxial cable, there is known a technology for reducing the size and cost by making innovative changes in the shape thereof (see Japanese published unexamined application No.2002-164132).
In order to connect a coaxial connector with a coaxial cable, a core as an inner conductor and a shield as an outer conductor of the coaxial cable are separated so that these are electrically connected respectively to predetermined terminals of the connector. As a result, the core of the coaxial cable is partly exposed out of the shield. In this state, in the case a high frequency signal at several gigahertz is transmitted through the coaxial cable, matching of characteristic impedances cannot be maintained, and VSWR deteriorates. Here, the characteristic impedance Z0 of a coaxial cable is expressed as follows.
                              Z          0                =                                            R              +                              j                ⁢                                                                  ⁢                2                ⁢                π                ⁢                                                                  ⁢                fL                                                    G              +                              j                ⁢                                                                  ⁢                2                ⁢                π                ⁢                                                                  ⁢                f                ⁢                                                                  ⁢                C                                                                        (        1        )                R: resistance of a coaxial cable per unit length [Ω/cm]    G: conductance of a coaxial cable per unit length [l/Ωcm]    L: inductance of a coaxial cable per unit length [H/m]    C: capacitance of a coaxial cable per unit length [F/m]However, at a high frequency, because resistance R and conductance G may be neglected, the characteristic impedance Z0 is determined by the ratio of inductance L and capacitance C. In the case the core of the coaxial cable is partly exposed out of the shield, the inductive reactance XL1 of the part of the core exposed out of the shield is added to the impedance Z0.XL1=2πfL  (2)Because the inductance L1 of the exposed part of the core is extremely small in value, when a transmission signal is at several hundred megahertz, the inductive reactance XL1 of the exposed part of the core can be neglected. However, with a transmission signal of gigahertz-class, the inductive reactance XL1 increases in value, hence making it impossible to neglect the inductive reactance XL1. Due to this, the characteristic impedance of the coaxial cable cannot to be maintained, and thereby the VSWR deteriorates.